Define quantitative pollutants.

The substances that cause pollution are called pollutants. These pollutants are broadly classified into two types, on the basis of their existence in nature:

> Quantitative pollutants- The substances that are naturally present in the environment but they become pollutants, when their concentration reaches beyond a threshold value in the environment because of human activities, form quantitative pollutants. Carbon dioxide is a good example of this, it is naturally present in the atmosphere but human activities like automobile emission are increasing its concentration in the atmosphere which is contributing to pollution and other harmful environmental effects.

> Qualitative pollutants- The substances that are not present in the environment naturally but are created by humans and cause pollution in the environment come under this category. For example, pesticides, insecticides, etc. these are chemicals produced by humans to get rid of insects and pests but they cause pollution as these are non-biodegradable in nature. 

Qualitative pollutants are further classified into two types-

- Biodegradable pollutant: The pollutants that get decomposed slowly and gradually over a time by the action of decomposers on it, are called biodegradable pollutants, for example, domestic waste.

- Non-biodegradable pollutants: These are the pollutants that do not decompose and accumulate in the environment, for example, plastic waste.